How to Generate Public and Private Keys on Windows, macOS, and Linux

Public and private keys are the cornerstones of modern cryptography, allowing secure communication and data protection. This guide will walk you through the process of generating public and private keys on Windows, macOS, and Linux, with detailed explanations for various key types.

Overview of Public and Private Keys

Public key cryptography, also known as asymmetric cryptography, uses a pair of keys: a public key and a private key. The public key can be shared with others and is used for encryption, while the private key is kept secret and is used for decryption.

There are several types of public and private key algorithms, including:

• RSA: A widely used algorithm that’s secure and versatile, supporting key lengths from 1024 to 4096 bits. RSA is often used for secure communication, digital signatures, and encryption.
• DSA: Digital Signature Algorithm, primarily used for creating and verifying digital signatures rather than encryption.
• ECDSA: Elliptic Curve Digital Signature Algorithm, an alternative to RSA and DSA that uses smaller keys for the same level of security.

Generating Keys on Windows

Using PuTTYgen

1. Download PuTTYgen from the official PuTTY website (https://www.putty.org/).
2. Open PuTTYgen and choose the desired key type (RSA, DSA, or ECDSA) from the “Parameters” section.
3. Select the desired key size (e.g., 2048 bits for RSA).
4. Click “Generate” and move your mouse randomly over the blank area to create entropy.
5. Once the key is generated, save the private key by clicking “Save private key” and the public key by selecting all the text in the “Public key for pasting into OpenSSH authorized_keys file” box.

Using OpenSSL (Windows Subsystem for Linux)

Follow the instructions for Linux (below) after installing the Windows Subsystem for Linux (WSL).

Generating Keys on macOS

Using Terminal

1. Open Terminal and enter the following command, replacing “KEY_TYPE” with “rsa”, “dsa”, or “ecdsa”, and “KEY_SIZE” with your desired key size (e.g., 2048 for RSA):

ssh-keygen -t KEY_TYPE -b KEY_SIZE

2. Follow the prompts to choose a save location and set a passphrase (optional).
3. The public and private keys will be saved in the specified location.

Generating Keys on Linux

Using Terminal

1. Open a terminal and enter the following command, replacing “KEY_TYPE” with “rsa”, “dsa”, or “ecdsa”, and “KEY_SIZE” with your desired key size (e.g., 2048 for RSA):

ssh-keygen -t KEY_TYPE -b KEY_SIZE

2. Follow the prompts to choose a save location and set a passphrase (optional).
3. The public and private keys will be saved in the specified location.

Now that you know how to generate public and private keys on various platforms, you can use them for secure communication, authentication, and encryption. Remember to keep your private keys safe and never share them with others.